Certain new types of vehicles, known as hybrid vehicles, employ a combustion engine coupled with a combination electric motor-generator to provide energy for vehicle locomotion. In some of these hybrid or mild-hybrid powertrain systems, an electric motor-generator system replaces the conventional starter motor and alternator. When the hybrid vehicle is decelerating or is stopped, the fuel flow to the engine is shut off to improve fuel economy. In contrast to a convention internal combustions engine, while the hybrid vehicle is at a standstill, the engine is not turning. The motor-generator system of the hybrid vehicle is implemented to enable this fuel cutoff feature while minimally affecting drivability.
In a mild-hybrid powertrain with an automatic transmission, when the brake pedal is released after a stop, the motor-generator system spins up the engine, and creeps the vehicle forward, similar to a conventional vehicle with an automatic transmission. The engine combustion can be commenced after some pre-determined period of time, or when the accelerator pedal is depressed. When the driver accelerates, the combustion engine restarts automatically and the hybrid vehicle can be driven in a conventional manner. When the combustion engine is running, the motor-generator acts as a generator to supply the hybrid electric vehicle's electrical power requirements, as well as recharging the on-board battery system. The vehicle's on-board battery system and a DCDC converter support the hybrid vehicle's electrical loads (fans, radio, etc) whenever the combustion engine is off.
While this new hybrid automotive design is advantageous from a fuel economy perspective, it can also present a need for additional design considerations. For example, it is necessary to periodically recharge the on-board battery pack in order for the hybrid vehicle to continue operating. There are presently at least three systems for charging the on-board battery pack of a hybrid vehicle. These three systems can be broadly characterized as follows: isolated charging systems; non-isolated charging systems; and integral charging systems.
The isolated charging systems employ a charger that incorporates a resonant converter type of power supply that allows electrical energy to be transformer-isolated from the vehicle battery during the charging cycle. Typical non-isolated charging systems do not generally employ the resonant converter topology for recharging the batteries. Finally, the typical integral charging system utilizes the motor windings and power electronics circuitry employed on the motor drive circuits to perform the battery-charging task. This approach typically includes the adoption of additional procedures in order to reduce the likelihood of delivering electrical power from the charging system to unintended locations.
While each of the previously mentioned charging systems has been adopted with some success, it should be noted that each of these systems also has certain limitations in the standard configuration. For example, in most typical conductive charging systems, a single contactor isolates the battery from the vehicle high-voltage system. This contactor is energized by the hybrid vehicle, both during vehicle propulsion and when the hybrid vehicle is receiving charging current from the off-board electric vehicle service equipment (EVSE). Since control of the electrical energy distribution during the charging sequence is considered desirable, these charging systems typically employ an isolation transformer to reduce the likelihood of inadvertent energy transfer.
During the typical charging sequence, other high-voltage loads usually serviced by the hybrid vehicle battery, such as air-conditioning, lighting and carious entertainment functions, can be brought on-line or taken off-line either automatically by the control system of the hybrid vehicle or by the vehicle operator. Additionally, the rating of the contactor is typically rated so as to be sufficient to handle the full battery current in the event of an anomaly involving either the charging system components or a high-voltage bus.
Yet another area of consideration with many battery-charging systems currently used in hybrid vehicles is the battery pack used to store the electrical power for the vehicle. Typically, the multiple inter-connections between the various components employ relatively expensive high-voltage cabling and connectors between the battery charger and the battery pack. The use of multiple, discrete components in the standard implementation generally means that control and signal cabling will be routed throughout the vehicle, possibly complicating the vehicle's electrical harness design and potentially increasing the cost of component integration and service.
Additionally, the pre-integration testing of the battery pack and associated control modules may become relatively complicated due to the typical industry practice of duplicating vehicle control functions in the manufacturing test environment. Further, the costs associated with integrating the modules into the electric vehicle and then performing various system-level test functions may be increased if the battery pack or the control modules fail the system level tests.
Finally, there are a continually developing set of requirements for battery charging systems driven not only by the practical considerations of the technology, but by various political situations. This includes various federal and state standards for battery charging systems that should also be considered in the design and implementation of new battery-charging systems. One example is the recent decision by the state of California Air Resource Board (CARB) to adopt a “zero-emissions” credit only for vehicles that utilize a conductive charging system in compliance with the Society of Automotive Engineers (SAE) standard known as SAE J1772. This decision contemplates the future ability of hybrid electric vehicles to actually provide surplus generated power from the vehicle to the larger local or even regional power grid in times of high utilization or emergency.
In view of the foregoing, it should be appreciated that it would be desirable to provide improved equipment and methods for charging the on-board battery module of a hybrid vehicle without adding significantly to the cost of the system. It is also desirable to more effectively control the energy distribution while charging the battery module. Additionally, compliance with various government standards is a desirable goal in order to maintain compatibility and enhance acceptance of new product designs. Furthermore, additional desirable features will become apparent to one skilled in the art from the foregoing background of the invention and following detailed description of a preferred exemplary embodiment and appended claims